Liquid biopsy tests produce conflicting results

A study has cast doubts on the reliability of ‘liquid biopsies’ – blood tests that detect tumour mutations and are increasingly used to guide treatment.

‘Our findings indicate that the output from genetic testing can differ markedly depending on which test is applied,’ the researchers wrote in JAMA Oncology. This can lead to different treatment recommendations, depending on which test was used.

The research was led by Professor Anthony Blau of the University of Washington and Dr Sibel Blau, a clinical oncologist. Patients were given two simultaneous tests – traditional tissue biopsy and novel liquid biopsy.

‘With a tumor biopsy, it’s like you read the book cover to cover. With a liquid biopsy, you read an entire shelf of books, but you only read the dust jackets,’ Dr Justin Odegaard, the senior medical director of Guardant Health, told The Atlantic.

The tests identified 45 mutations in total within the patient group. But only 10 mutations (22 percent) were discovered by both platforms. This meant that the tests gave different drug recommendations to the majority of patients.

The new study only tested nine patients, but the findings match other work. A paper from researchers at Northwestern looking at liquid versus tissue biopsies reported that over half of the mutations found by one test did not show up in the other.

Which test is more accurate? ‘There is no easy answer,’ Dr Richard Schilsky, the chief medical officer of the American Society of Clinical Oncology, told The Atlantic. ‘Because nobody actually knows what is the truth in terms of what’s happening inside a person’s tumor throughout the body.’

Dr Sibel Blau added that she thinks liquid biopsies ‘are not really ready for primetime’ and that clinicians should rely on tissue biopsy results until there is more research on the effectiveness of liquid biopsies.

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What is Exosome RNA?

Exosomes are cell-derived vesicles that are present in many and perhaps all biological fluids, including blood, urine, and cultured medium of cell cultures. Exosomes contain various molecular constituents of their cell of origin, including proteins and RNA. It is becoming increasingly clear that exosomes have specialized functions and play a key role in, for example, coagulation, intercellular signaling, and waste management. - from wikipedia